Oriented polypropylene film with improved blocking resistance

ABSTRACT

The present disclosure is directed to a film formulation that resulted in a substantially non-migratory cold seal release film with improved blocking resistance. Specifically, the multilayered biaxially oriented polypropylene film can include a core layer of polypropylene homopolymer; a first outer layer on one side of the core layer that can be suitable for sealing, printing, or coating; and a second outer layer on the opposite side of the core layer that is a blocking resistant layer comprising thermoplastic polymers which reduce blocking tendency.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.15/940,135, filed Mar. 29, 2018, the entire contents of each of whichare incorporated herein by reference.

FIELD OF THE DISCLOSURE

This disclosure relates to an oriented polypropylene film with improvedblocking resistance. More specifically, this disclosure relates to acold seal release film with an outer release layer that providesblocking and scuff resistance.

BACKGROUND OF THE DISCLOSURE

Cold seal release films are most commonly used for the outside of amultilayered packaging structure needed to be sealed under lowtemperature region. The cold seal release film should not form acohesion with a cold seal adhesive layer coated onto the opposite sideof the multilayered laminated packaging structure when the film is woundinto a roll. As such, blocking is the unwanted adhesion between the coldseal adhesive layer and the release layer under the conditions ofpressure and aging.

U.S. Pat. No. 4,925,728 describes a method of producing a fineparticle-pigmented BOPP release film comprising a core layer ofpolypropylene homopolymer and two top release layers consisting of 98.5to 99.6 wt % of polypropylene homopolymer and 0.4 to 1.5 wt % ofpolydiorganosiloxane.

Patent Application WO 1995015850A1 discloses a release label stockcomprising a substrate of oriented high crystalline polypropylene and arelease coating material which is an electron beam curablesilicone-acrylate release material.

U.S. Pat. No. 6,465,107 describes a method of producing siliconecontaining LDPE resins by chemical grafting reaction and a method ofincorporating a silicon-containing LDPE resin into a laminate as anouter layer by coextrusion.

U.S. Pat. No. 7,105,233 describes a method of using organo-modifiedpolydialkylsiloxane to greatly reduce the migration of silicone oils byincorporating large alkyl groups into siloxane backbone.

U.S. Pat. Nos. 6,074,762; 6,472,077; and 6,682,822 describe a type ofthe outer layer of polymers based on homopolymer PP, HCPP, and HDPE,comprising essentially homopolymer or a blend of homopolymers ofethylene or propylene with silicone oils and ultra high molecular weightsilicone (silicone gum) at an amount of 0.05 to 10 wt % in the releaselayer. Silicone oil transfer and contamination are still a problemresulting from masterbatches of silicone oils with lower viscosity.

U.S. Pat. Nos. 5,981,047; 5,798,174; 5,489,473; and 5,792, 549 describea type of cold seal release film with butene-based release materialsessentially consisting of polybutene homopolymers and a blend of randomcopolymers or terpolymers of ethylene, butene, or propylene monomers.The release layer of the films has poor scuff resistance.

U.S. Pat. No. 5,840,419 describes a method of making printable BOPPfilms with two outer layers comprising ethylene-propylene copolymer andpartially cross-linked polydimethylsiloxane.

SUMMARY OF THE DISCLOSURE

Applicants have discovered an economical method to improve blockingresistance of cold seal release films using stiff high crystallinepolymers and avoid using migratory additives and soft release materialsin the outer release layer. Specifically, none of the references citedabove demonstrated that a combination of high crystalline polypropyleneand low ethylene containing polybutene-1 can result in excellent releaseproperties to a cold seal adhesive layer. In addition, partiallycrosslinked polydialkylsiloxane can efficiently lower and stabilize thecoefficient of friction (“COF”) of the outer release layer, greatlyavoiding silicone oil, and silicone moieties contamination or transfer.

Blocking can be prevented by using anti-blocking agents and specialthermoplastic polymers which can reduce the tendency of forming cohesionwith cold seal adhesives—either natural rubber latex or synthetic rubberlatex, which are rubbery materials with glass transition temperatures(Tg) lower than 0° C. Some polyolefin thermoplastic polymers andadditives demonstrate blocking resistance to cold seal adhesives orpressure sensitive adhesives when they are incorporated into an outerlayer of a film with a direct contact to a cold seal adhesive layer. Thespecial polyolefin thermoplastic polymers can include high crystallinepolypropylene (“HCPP”, high crystallinity, isotactic content 95% orgreater, Tg=0˜15° C.) homopolymers, high density polyethylene (“HDPE”,high crystallinity, Tg=−125° C.) homopolymers, and butene-1 containingpolymers (Tg=−18° C.). The special additives can include crosslinkedsilicones and silicone-grafted polyolefins which have a low tendency totransfer to the opposite side of the film.

Silicones also known as polydialkylsiloxanes (most commonly used arepolydimethylsiloxane (“PDMS”)) have a unique chemical structure that hasa backbone of silicon-oxygen (Si—O) linkages. Polydimethylsiloxane has alow glass transition temperature (Tg=−125° C.) and can be used as slipand release agents. Commercially available are silicone fluids (siliconeoil and gum types of silicones) with a viscosity of from 0.65 to2,500,000 cSt, partially cross-linked particles, fully cross-linkedparticles, and grafted silicone containing polyolefin polymers.Crosslinking of the polymers can significantly increase glass transitiontemperature. Both non-crosslinked silicone fluids and cross-linkedsilicones not only can provide good release properties but can alsoreduce the coefficient of friction of the surface layer. The differencein physical properties (especially shape and hardness) of thosecrosslinked and partially crosslinked silicones can show very differentslip and release performance as they are used in the outer layer of afilm. The drawbacks of these liquid-like silicones can include theusually undesirable cross-contamination resulting from low molecularweight silicone moieties or silicone oils transferred to the oppositeside of a film.

In some embodiments, a cold seal release film includes a core layercomprising polypropylene; a first outer layer on a side of the corelayer comprising polyolefin resin; and a second outer layer on a side ofthe core layer opposite the first outer layer comprising conventionalpolypropylene, high crystalline polypropylene, medium densitypolyethylene, or high density polyethylene; up to 40 wt. % polybutene-1;and 0.75-2.5 wt. % partially crosslinked polydialkylsiloxane. In someembodiments, the medium or high density polyethylene has a density of0.93-0.97 g/cm³. In some embodiments, the polybutene-1 is lowethylene-containing polybutene-1. In some embodiments, the lowethylene-containing polybutene-1 has an ethylene content of less than 2mol %. In some embodiments, the low ethylene-containing polybutene-1 hasa melt flow rate of 2 to 6 g/10 min. In some embodiments, the secondouter layer comprises 2.5-40 wt. % polybutene-1. In some embodiments,the second outer layer comprises spherical anti-blocking agents. In someembodiments, the second outer layer comprises 1000-5000 ppm sphericalanti-blocking agents. In some embodiments, the spherical anti-blockingagents comprise at least one of crosslinked silicone polymers andsynthetic SiO2. In some embodiments, the partially crosslinkedpolydialkylsiloxane is partially crosslinked polydimethylsiloxane. Insome embodiments, the second outer layer has a dynamic coefficient offriction of 0.20-0.35. In some embodiments, the polypropylene in thecore layer is high crystalline polypropylene. In some embodiments, thecore layer comprises 2.5-25 wt. % hydrogenated hydrocarbon resins. Insome embodiments, the core layer comprises 1-1000 ppm of antistaticadditives. In some embodiments, the polyolefin resin comprises ethylenehomopolymer, propylene homopolymer, ethylene or propylene-basedcopolymers and terpolymers, or blends thereof. In some embodiments, aside of the second outer layer opposite the core layer isdischarge-treated using high densities of energy flux. In someembodiments, a side of the first outer layer opposite the core layer isdischarge-treated.

In some embodiments, a method of forming a cold seal release filmincludes coextruding a laminate comprising: a core layer comprisingpolypropylene; a first outer layer on a side of the core layercomprising polyolefin resin; and a second outer layer on a side of thecore layer opposite the first outer layer comprising conventionalpolypropylene, high crystalline polypropylene, medium densitypolyethylene, or high density polyethylene; up to 40 wt. % polybutene-1;and 0.75-2.5 wt. % partially crosslinked polydialkylsiloxane; andbiaxially orienting the coextruded laminate. In some embodiments, themedium or high density polyethylene has a density of 0.93-0.97 g/cm³. Insome embodiments, the polybutene-1 is low ethylene-containingpolybutene-1. In some embodiments, the low ethylene-containingpolybutene-1 has an ethylene content of less than 2 mol %. In someembodiments, the low ethylene-containing polybutene-1 has a melt flowrate of 2 to 6 g/10 min. In some embodiments, the second outer layercomprises 2.5-40 wt. % polybutene-1. In some embodiments, the secondouter layer comprises spherical anti-blocking agents. In someembodiments, the second outer layer comprises 1000-5000 ppm sphericalanti-blocking agents. In some embodiments, the spherical anti-blockingagents comprise at least one of crosslinked silicone polymers andsynthetic SiO2. In some embodiments, the partially crosslinkedpolydialkylsiloxane is partially crosslinked polydimethylsiloxane. Insome embodiments, the second outer layer has a dynamic coefficient offriction of 0.20-0.35. In some embodiments, the polypropylene in thecore layer is high crystalline polypropylene. In some embodiments, thecore layer comprises 2.5-25 wt. % hydrogenated hydrocarbon resins. Insome embodiments, the core layer comprises 1-1000 ppm of antistaticadditives. In some embodiments, the polyolefin resin comprises ethylenehomopolymer, propylene homopolymer, ethylene or propylene-basedcopolymers and terpolymers, or blends thereof. In some embodiments, themethod further includes discharge-treating a side of the second outerlayer opposite the core layer using high densities of energy flux. Insome embodiments, the method further includes discharge-treating a sideof the first outer layer opposite the core layer.

In some embodiments, the release layer of the coextruded release filmcomprises a blend of 75 to 99.8 wt % high crystalline polypropylene(HCPP, isotactic content ≥95%) and 1 to 25 wt % low ethylene containingbutene-1 polymers, and 0.2 to 1.5 wt % crosslinked silicone polymerparticles or synthetic silica (SiO2) particles. In some embodiments, therelease layer of the coextruded release film comprises a blend of 1 to99.8 wt % high crystalline polypropylene (HCPP, isotactic content ≥95%)and 1 to 25 wt % low ethylene containing butene-1 polymers (PB-1), and0.2 to 0.5 wt % crosslinked silicone polymer particles or 0.1 to 3 wt %partially crosslinked polydialkylsiloxane particles. In someembodiments, the release layer of the coextruded cold seal release filmcomprises a blend of 0 to 99.8 wt % high crystalline polypropylene(HCPP, isotactic content ≥95%), 0 to 99.8 wt % high density polyethylene(HDPE), and 0 to 40 wt % low ethylene containing PB-1 polymers, 0 to 40wt % the random copolymers of ethylene, propylene or butene-1, and 0.2to 5.0 wt % crosslinked silicone polymer particles or partiallycrosslinked polydialkylsiloxane particles. In some embodiments, therelease layer of the coextruded cold seal release film comprises a blendof 60 to 99.8 wt % high density polyethylene (HDPE) and 1 to 40 wt % lowethylene containing PB-1 polymers, and 0.2 to 0.5 wt % crosslinkedsilicone polymer particles, and 0.1 to 3 wt % partially crosslinkedpolydialkylsiloxane particles.

Additional advantages will be readily apparent to those skilled in theart from the following detailed description. The examples anddescriptions herein are to be regarded as illustrative in nature and notrestrictive.

All publications, including patent documents, scientific articles anddatabases, referred to in this application are incorporated by referencein their entirety for all purposes to the same extent as if eachindividual publication were individually incorporated by reference. If adefinition set forth herein is contrary to or otherwise inconsistentwith a definition set forth in the patents, applications, publishedapplications and other publications that are herein incorporated byreference, the definition set forth herein prevails over the definitionthat is incorporated herein by reference.

DETAILED DESCRIPTION OF THE DISCLOSURE

Blocking resistance and machinability can be crucial factors of the coldseal release films required by the end users. To achieve the objects ina cost-effective manner, Applicants discovered a cold seal release layerusing thermoplastic polymers with resistance against forming cohesionwith cold seal adhesives.

Cold seal adhesives are made from synthetic and natural rubbery resinsand latexes as well as using effective anti-blocking and slip agents forcontrol of coefficient of friction (COF) properties. In addition, coldseal adhesives are amorphous rubbery materials (Tg<0° C.) which are verysticky and tacky under ambient temperature environment. They are usuallyapplied as a water-bourne latex coating onto an article (such as a filmor laminate). The materials on the outer surface of a cold seal releaselayer can include those which are incompatible (e.g. HCPP crystals) withthe cold seal adhesive layer; those which are compatible (e.g. amorphousrubbery resins, e.g. polymer tails (which are low molecular weightrubbery species)) with cold seal adhesive layer; those which are nottransferable (e.g. firmly embedded inorganic anti-blocking and slipadditives (do not adhere to the cold seal adhesive layer)), and thosewhich are transferable (e.g. free particles on the top surface: e.g.silicone oils, migratory waxes and unimbedded anti-blocking and slipadditives).

The material domains on the top surface of the outer release layer caninclude polymer crystals, amorphous polymer phase, embeddedanti-blocking particles (do not adhere to the cold seal adhesive layer),debris of small molecules, rubbery or moveable polymer chain segments ortails. Both free particles (migratory) and rubbery materials can have astrong tendency to “deaden” the cold seal strength of the cold sealadhesive layer coated on the receptive substrate. “Deadening” of a coldseal adhesive means that the adhesive strength of the cold seal isweakened from contamination of the cold seal. Free particles and debrisof small molecules can have a tendency to transfer onto the cold sealadhesive layer, resulting in contamination. The amorphous materials'said rubbery amorphous polymer domains, chain segments, and tails on thetop surface can have a tendency to form cohesion with the molecules ofthe cold seal adhesive layer. Both surface contamination and cohesioncould significantly deaden the cold sealing performance of a coldsealable laminate film.

The cold seal release films disclosed herein can include a core layer(B); a first outer layer (A) that can be a functional layer formulatedto have properties of heat sealing, winding, adhesion, coating, and/orprinting; and a second outer layer (C) that can be a release layer toprovide blocking and scuff resistance. The laminate film can becoextruded and then oriented either uni-axially or biaxially in both themachine and transverse directions.

In some embodiments, the coextruded laminate release film could be a twolayer film comprising a core layer and an outer release layer. The outersurface of the core layer opposite to the release layer can bedischarge-treated for higher surface energy functionalities.

In some embodiments, intermediate layer(s) (D and F) comprisingthermoplastic polymers can be incorporated into the structure betweenthe core layer and at least one outer layer of the coextruded releasefilm as special intermediate functional layers. The coextruded releasefilm could have a four or five layer structure of A/D/B/C, A/B/D/C,A/D/B/D/C, AB/D/F/C, and A/D/F/B/C; other permutations could becontemplated as well. The intermediate layers could be used as thefunctional structure layer of adding gas barrier such as a layer ofEVOH, adding migratory additives, or providing a function of cavitationor pigmentation.

The outer release layers disclosed herein can have various components.For example, high crystalline polypropylene (“HCPP”) homopolymers canprovide advantages of high stiffness, high modulus, and low residues(isotactic content ≥95%) compared to conventional polypropylene (“PP”)homopolymers (isotactic content <95%, typically 90-93%). HCPP polymersare usually used as the core resin of making oriented stiff films andbarrier packaging films. HCPP polymers can be difficult to uniformlyorient along both machine and transverse direction during orientationprocesses. Commonly, processing aids, including hydrocarbon resins,polyolefin waxes, polyolefin copolymers or terpolymers of such asethylene, propylene and butene can be added into HCPP core layer or baselayer of a film at an amount of about 3 to 15 wt % of the layer blendfor improving processability.

Polypropylene homopolymers used in the outer release layer ofmultilayered thermoplastic films can be able to provide excellentscratch and abrasion resistance due to the high surface crystallinity(hardness) of the outer top surface and relatively high Tg. Acombination of high isotacticity, low xylene solubles (low molecularweight amorphous residues typically <3 wt % of the polymer, morepreferably less than 2.5 wt. %), and high content of PP crystals on thetop surface of the outer release layer can make the outer release layerdifficult to form cohesion with the cold seal adhesive layer at theinterfacial boundary. In comparison, both amorphous/rubbery materials(with high softness) and homopolymers with lower crystallinity (e.g.<95% isotacticity) and high xylene solubles (e.g. >3 wt % xylenesolubles) on the top surface of an outer layer can have strong tendency(due to increased compatibility with rubbery adhesives) to form cohesionwith the rubbery cold seal adhesive layer at the interfacial boundary asthey have direct contact under high pressure and storage conditions,elevated temperature (e.g 50° C.) storage conditions, and lengthystorage times (e.g. 1 month to 1 year storage). High interfacialseparation force (blocking force) during unwinding of a cold sealadhesive-coated film roll could deteriorate the cold sealing strength ofa cold seal adhesive layer by stripping off the cold seal adhesive fromthe cold seal receptive layer to the cold seal release layer. Inaddition, there can be the danger of the cold seal adhesive-coated rollblocking entirely such that the film layers cannot be separated at alland thus, cannot be unwound for further processing.

In some embodiments, the HCPP can be in an amount of less than about99.8 wt. %, 99 wt. %, about 95 wt. %, about 90 wt. %, about 85 wt. %,about 75 wt. %, about 65 wt. %, about 55 wt. %, or about 50 wt. % of theouter release layer. In some embodiments, the HCPP can be in an amountof more than about 50 wt. %, about 55 wt. %, about 65 wt. %, about 75wt. %, about 85 wt. %, about 90 wt. %, about 93 wt. %, about 95 wt. %,or about 99 wt. % the outer release layer. In some embodiments, the HCPPcan be about 50-99.8 wt. %, about 55-98 wt. %, about 65-98 wt. %, about75-99 wt. %, about 85-99 wt. %, about 90-99 wt. %, about 91-95 wt. %, orabout 92-94 wt. % of the outer release layer.

Examples of suitable HCPP homopolymers can include Total 3270, Total3273, Phillips 66 CH020XK, and Braskem Inspire® 6025. Those HCPP resinscan have xylene solubles at less than about 3 wt. %, less than about 2.5wt. %, or about 2 wt %, isotactic content of >95% (preferably 98% ormore) and MFR from about 2 to 4 g/10 min or about 2 to 3 g/10 min (2.16Kg/230° C.), characterized by low content in residues and polymer tails.The HCPP can have isotactic content greater than or equal to 95%.

Orientation of HCPP polymer outer layers can be very challenging withoutadding processing aids, especially, as the HCPP resin has a low meltflow rate (high molecular weight and isotacticity). The HCPP outer layercould have extremely high surface roughness and irregular stretch marksdue to low flowability of HCPP polymers in the skin layer during thebiaxial orientation tentering process. Conventional processing aidsincluding HCR, migratory additives, and elastomers are undesirable foradding to the HCPP-comprising outer cold seal release layer since theyincrease tendency to form cohesion (blocking) with the cold sealadhesive layer.

Surprisingly, Applicants discovered that polybutene polymers (e.g., PB-1polymers) can be used as a processing aid to improve the flowability ofHCPP polymers in the outer release layer at a low concentration which isthe range of peel-seal and non-peelable regions of a sealable-peelablefilm. The polybutene in the outer release layer may not deteriorate therelease performance of the HCPP polymers. To the contrary, polybutenecan eliminate the negative influence of the carrier resin—e.g.homo-polypropylene and propylene copolymers—used to produce thecommercial masterbatches of anti-blocking and slip agents typicallyadded to these outer layers, such that the danger of cold seal deadeningin a finished laminate roll can be avoided.

Polybutene polymer at an amount of less than about 40 wt % of the outerrelease layer was found to improve the stretchability and releasabilityof HCPP release layer due to its unique physical properties. In someembodiments, the polybutene polymer can be in an amount of less thanabout 40 wt. %, about 30 wt. %, about 25 wt. %, about 20 wt. %, about 10wt. %, about 5 wt. %, or about 2.5 wt. % of the outer release layer. Insome embodiments, the polybutene polymer can be in an amount of morethan about 2.5 wt. %, about 5 wt. %, about 10 wt. %, about 20 wt. %,about 25 wt. %, about 30 wt. %, or about 40 wt. % the outer releaselayer. In some embodiments, the polybutene polymer can be about 1-40 wt.%, about 2.5-40 wt. %, about 2.5-30 wt. %, about 2.5-25 wt. %, about2.5-20 wt. %, about 2.5-15 wt. %, or about 5-15 wt. % of the outerrelease layer. In some embodiments, the polybutene polymer can be about1-40 wt. %, about 20-40 wt. %, about 25-40 wt. %, or about 30-40 wt. %of the outer release layer.

In some embodiments, the polybutene polymer can be a lowethylene-containing polybutene-1 (“PB-1”) polymer. Examples of suitablePB-1 polymers can include LyondellBasell Toppyl® PB8340M and PB8640Mpolymers. Toppyl® PB8340M and PB8640M are random copolymer of butene-1with low ethylene content (<2 mole %). They have a melt flow rate of 1.0g/10 min. and 4.0 g/10 min. (2.16 Kg/190° C.), respectively, and twomelting temperatures 97° C. and 114° C. In some embodiments, thepolybutene polymer can have an ethylene content of less than about 2 mol%. In some embodiments, the polybutene polymer can have a melt flow rateof about 2-6 g/10 min (2.16 Kg/190° C.). The melting temperature (Tm) oflow ethylene-containing PB-1 polymers such as the brands ofLyondellBasell Toppyl® PB8640M and PB8340M is in the range of about 97to 114° C., and the melting temperature of HCPP is about 165° C. Assuch, PB-1 polymers melt at temperatures lower than the melting point ofHCPP. In addition, as a result of similarity in structure, PB-1 polymersand HCPP are compatible. Thus, a desirable amount of PB-1 polymer couldbe well dispersed in the HCPP matrix. Without being bound by any theory,it is thought that PB-1 polymer can help to “lubricate” the stretchingof HCPP crystals during the tentering process of oriented film-making.The stretching temperature of the coextruded film is often higher thanthe T_(m) of PB-1 polymers, but lower than the Tm of HCPP crystals.After orientation, HCPP can crystallize at higher temperatures, followedby PB-1 crystallization in the amorphous phase of HCPP in the outerlayer as cooling continues. As a result of this factor, PB-1 crystalislands or domains can be well dispersed inside the amorphous phase of apredominately HCPP layer which has a tendency to reduce blocking forceto cold seal adhesive layer.

Furthermore, polybutene polymers at amounts described above in the outerrelease layer can also be used as a processing aid for polyethylenepolymers to improve stretchability and releasability. Examples ofsuitable polyethylene resins can include medium density polyethyleneand/or high density polyethylene (“HDPE”) with a density of about 0.93to 0.97 g/cm³ (e.g., Total Petrochemicals HDPE9260 and Dow ChemicalsDOWLEX™ 2027G) and a melt flow rate of about 1 to 6 g/10 min (2.16kg/190° C.). HDPE9260 has a melt flow rate of 2.0 g/10 min. and adensity of 0.96 g/cm³ and a melting point of 135° C. DOWLEX2027G has amelt flow rate of 4 g/10 min. and a medium density of 0.94 g/cm³ and amelting point of 127° C.

In some embodiments, the polyethylene can be in an amount of less thanabout 99.8 wt. %, 99 wt. %, about 95 wt. %, about 90 wt. %, about 85 wt.%, about 75 wt. %, about 65 wt. %, about 55 wt. %, about 50 wt. %, about40 wt. %, about 35 wt. %, or about 30 wt. % of the outer release layer.In some embodiments, the polyethylene can be in an amount of more thanabout 30 wt. %, about 35 wt. %, about 45 wt. %, about 50 wt. %, about 60wt. %, about 70 wt. %, about 80 wt. %, about 85 wt. %, or about 90 wt. %the outer release layer. In some embodiments, the polyethylene can beabout 1-99.8 wt. %, about 30-95 wt. %, about 35-90 wt. %, about 50-90wt. %, about 75-90 wt. %, about 80-90 wt. %, or about 85-90 wt. %

In some embodiments, the outer release layer can include conventionalpolypropylene. Examples of suitable conventional homopolypropylene(“PP”) resins include Total Petrochemical Total 3271 and Total 3274,Phillipps 66 CH016 and CH020-01. In some embodiments, the PP can be inan amount of less than about 99 wt. %, about 95 wt. %, about 90 wt. %,about 85 wt. %, about 75 wt. %, about 65 wt. %, about 55 wt. %, or about50 wt. % of the outer release layer. In some embodiments, the PP can bein an amount of more than about 50 wt. %, about 55 wt. %, about 65 wt.%, about 75 wt. %, about 85 wt. %, about 90 wt. %, about 93 wt. %, orabout 95 wt. % the outer release layer. In some embodiments, the PP canbe about 50-99 wt. %, about 55-98 wt. %, about 65-98 wt. %, about 75-99wt. %, about 85-99 wt. %, about 90-99 wt. %, about 91-95 wt. %, or about92-94 wt. % of the outer release layer.

In some embodiments, a matte-finish film surface could be achieved byadding incompatible polymers or block copolymers of ethylene and/orpropylene into the outer release layer, and additives with highrefractive index. Polymer flow in the outer release layer couldphysically roughen the surface roughness and raise the haze of the outersurface due to significant difference in refractive index. Examples ofsuitable matte finish materials include POLYBATCH® DUL 3636 LTX-3 and3636 DUL LT2 masterbatches, supplied by A. Schulman, and Ampacet 403687and PC523A masterbatches supplied by Ampacet. Those proprietarymatte-finish masterbatches are compatible with PP block copolymer, PPhomopolymer, PP random copolymer, HDPE, and MDPE. In some embodiments,the matte resin masterbatch can be in the outer release layer in anamount of at least 25 wt. %, about 35 wt. %, about 45 wt. %, about 50wt. %, about 55 wt. %, about 60 wt. %, about 65 wt. %, about 70 wt. %,or about 75 wt. %. In some embodiments, the matte resin masterbatch canbe in the outer release layer in an amount of at most about 75 wt. %,about 70 wt. %, about 65 wt. %, about 60 wt. %, about 55 wt. %, about 50wt. %, about 45 wt. %, about 35 wt. %, or about 25 wt. %. In someembodiments, the matte resin masterbatch can be in the outer releaselayer in an amount of about 25-75 wt. %, about 35-75 wt. %, about 45-75wt. %, about 50-70 wt. %, or about 55-70 wt. %. To achieve satisfactorymatte finish, a skin layer of ca. 2 microns can be extruded for a 12 to15 micron thick films and 3 microns for films of more than 15 micronstotal thickness. In some embodiments, for achieving a matte finish, thecold seal release layer comprises predominantly a blend of HCPP, HDPE,and propylene block copolymers and anti-blocking and slip additives aswell as compositions that improve blocking resistance.

Anti-blocking and slip agents can also be important to reduce blockingforce and COF. These antiblocking and slip agents include sphericalanti-blocking particles, such as synthetic SiO2 (e.g. SYLOBLOC® silica),crosslinked silicones (e.g. Tospearl® crosslinked silicone polymermicrosphere particles), and partially crosslinked polydialkylsiloxaneparticles. Low and stable COF can be important for achieving goodmachinability of a cold seal release film. The coextruded outer skinlayers (A and C) on both sides of the core layer (B) can have athickness after biaxial orientation between about 0.1 and 3 μm, betweenabout 0.5 and 1.5 μm, or between about 0.5 and 1.0 μm. A desirableamount of anti-blocking and/or slip agents may be added up to about50,000 ppm to an outer layer. In some embodiments, about 300-5000 orabout 2000-3500 ppm of anti-blocking agent and/or slip agents may beadded to at least one outer layer. In some embodiments, the antiblockand/or slip additives used in the film are non-migratory.

Suitable inorganic anti-blocking and slip agents for the outerfunctional layer can include those such as spherical inorganic silicasand sodium calcium aluminosilicates. Suitable organic anti-blockingagents can include those such as cross-linked silicone polymers(polymethylsilsesquioxane, e.g. Momentive Tospearl® particles) andpolymethylmethacrylate (PMMA particles), and partially cross-linkedpolydialkylsiloxane particles. Typically, desirable particle sizes ofthese anti-blocking agents can in the range of from about 1-12 μm, about1-6 μm, about 2-5 μm, or about 2-4 μm.

Suitable anti-blocking and slip agents for the outer release layer caninclude those having smooth surface, low surface energy, and lowtendency to transfer and stick to the adhesive layer, includingspherical silica particles (SiO2) and cross-linked silicone polymerparticles (Tospearl® particles). The particle sizes can be in the rangeof from 1-12 μm, about 1-6 μm, about 2-5 μm, or about 2-4 μm.

Suitable anti-blocking and slip agents can also include partiallycrosslinked polydialkylsiloxane particles, which have irregular particlesurface, low surface energy, and non-flowable physical property;crosslinked silicone polymer particles; synthetic silica (SiO2)particles. The potential silicone oligomer residues/moieties inside thepartially cross-linked particles can be greatly confined in theparticles so that the content of mobile silicone oligomers is notsubstantially detrimental to the functionalities of the outer functionallayer (A) and the cold sealing performance of the cold seal adhesivelayer. The partially cross-linked polydialkylsiloxane particles can havethe slip attribute of silicone oil but not the transference andcontamination issues to the cold seal adhesive layer. Preferably, theparticle sizes can be controlled in the range of about 0.5 to 10 micronsand more preferably in the range of from 0.5 to 4 microns.

Partially cross-linked polydialkylsiloxane can be produced by reactiveextrusion compounding process using silica treated functionalizedsilicone gum (ultra high molecular weight siloxane), initiator, andpropylene homopolymer or copolymers. Examples of those partiallycross-linked silicone gum can include EverGlide® MB-125-11 Ultra andX116EPC, provided by Polymer Dynamix. The active composition ofpolydialkylsiloxane in MB125-11 and X116EPC is about 25 wt % of themasterbatch. The carrier resins used in compounding MB125-11 and X116EPCwere conventional homo-polypropylene and propylene copolymer,respectively. In some embodiments, the partially crosslinkedpolydialkylsiloxane can be partially crosslinked polydimethylsiloxane(“PDMS”). Examples of suitable partially crosslinked polydialkylsiloxanecan also include Dow Corning HMB-630. The active content in HMB-6301 is25 wt % in homo-PP carrier resin of the masterbatch. Besides partiallycrosslinked polydialkylsiloxane, a silica treated high molecular weightsiloxane polymer can be used in the release layer. Dow Corning MB50-801is an example of a silica modified high molecular siloxane polymerdispersed in propylene homopolymer and the active content in MB50-801 isabout 50 wt %. In some embodiments, the active content in themasterbatch can be about 10-50 wt. %. The particle size of partiallycross-linked silicone after the film is made is predominately in therange of from about 0.25 to 10 microns, about 0.5 to 4 microns, or about0.5 to 2 microns.

In some embodiments, the amount of partially crosslinkedpolyalkylsiloxane, silica modified high molecular weight siloxanepolymer, crosslinked silicone polymer particles and/or synthetic silica(SiO2) particles in the cold seal release layer can be in the range ofabout 0.1 to 3 wt %, about 0.2-1.5 wt. %, about 0.4 to 2.5 wt %, about0.75-2.5 wt. %, about 0.75-1.75 wt. %, 0.75-1.25 wt. %, 0.75-1 wt. %,about 0.2-0.5 wt. %, or about 0.4-1.5 wt. %. In some embodiments, thetotal content of the antiblocking and slip agents in the outer releaselayer is less than 3 wt. %.

In some embodiments, the anti-blocking and/or slip agent can be in therelease layer as a masterbatch containing a certain amount of theanti-blocking and/or slip agent. In some embodiments, the anti-blockingagent and/or slip agent masterbatch can be in the outer release layer inan amount of at least about 1 wt. %, about 2 wt. %, about 3 wt. %, about4 wt. %, about 5 wt. %, about 6 wt. %, about 7 wt. %, about 8 wt. %,about 9 wt. %, or about 10 wt. %. In some embodiments, the anti-blockingagent and/or slip agent masterbatch can be in the outer release layer inan amount of at most about 15 wt. %, about 12 wt. %, about 10 wt. %,about 9 wt. %, about 8 wt. %, about 7 wt. %, about 6 wt. %, about 5 wt.%, about 4 wt. %, about 3 wt. %, or about 2 wt %. In some embodiments,the anti-blocking agent and/or slip agent masterbatch can be in theouter release layer in an amount of about 1-15 wt. %, 2-10 wt. %, or4-10 wt. %.

Suitable migratory anti-blocking, antistatic, and slip agents could alsobe incorporated into the intermediate layer or core layer of thecoextruded film at a desirable amount. Examples of those includestearates, fatty amides, and silicone oils of low molecular weightmolecules, and blends thereof. Examples of suitable migratory additivescan include tertiary amines, stearamide, erucamide, behenamide, glycerolmonostearate, and blends thereof. Preferably, a desirable amount of from1 to 2000 ppm migratory additives is added into the core layer orintermediate layer, more preferably, the content of migratory additivein the core or intermediate layer is in the range of from 1 to 1000 ppm.

Suitable examples of thermoplastic polymers for the outer functionallayer include homopolymers of polypropylene and polyethylene resins suchas Total3571, Dow DOWLEX2027G, mini-random polypropylene polymer such asLX11203, propylene copolymers such as Total 8473, and ExxonMobilVistamaxx 3588FL and Basell Adsyl 7416 XCP, copolymers and terpolymersof ethylene, propylene and butene, and blends thereof.

Furthermore, an optional but desirable amount of fluoropolymer additivecan be included in the outer layers to improve the distribution ofadditives and prevent die lip buildup. The content of the fluoropolymeradditive can be in the range of about 100-1000 ppm of the outer or corelayer, preferably 300-600 ppm of the core or outer layer. Thefluoropolymer is commercially available in a masterbatch form.

The core layer (B) of the coextruded laminate film can comprisepropylene homopolymers. Examples of suitable conventionalhomopolypropylene (PP) resins can include Total Petrochemical Total 3271and Total 3274, Phillipps 66 CH016 and CH020-01. Examples of suitablehigh crystalline polypropylene resins (HCPP) can include Phillips 66CH020XK, Total Petrochemical Total 3270 and Total 3273. Typically, thesepolypropylene resins can have a melt flow rate in the range of from 1.5to 3.5 g/10 min., a melting point in the range of from 160-167° C., anda density of about 0.90-0.92 g/cm³. Typically, isotactic content of theHCPP resins can be at least 95% (as measured by ¹³C NMR spectra obtainedin 1,2,4-trichlorobenzene solutions at 130° C.; the % isotactic can beobtained by the intensity of the isotactic methyl group at 21.7 ppmversus the total (isotactic and atactic) methyl groups from 22 to 19.4ppm) and xylene solubles can be less than 3%. The CH020XK, supplied byPhillips 66, is highly isotactic crystalline polypropylene resin (HCPP)and has a melt flow rate of 2.2 g/10 min. (2.16 Kg/230° C.), a meltingtemperature of 165° C., and xylene solubles of about 2%. CH020-01 homoPPhas a melt flow rate of about 2.0 g/10 min. a melting temperature ofabout 161° C., and xylene solubles of about 4.3 wt %.

As HCPP is used as the core layer resin, an optionally desirable amountof hydrogenated hydrocarbon resin can be added into the core layer as aprocessing aid at an amount of from about 2.5 to 25 wt % or about 5 to15 wt % of the weight of the core layer. Examples of suitablehydrogenated hydrocarbon resins can include Plastolyn® R1140 andEastotac® H-142W provided by Eastman Chemicals; Oppera® PR100A providedby ExxonMobil. Typically, these hydrocarbon resins can be fullyhydrogenated water-white amorphous materials having a softening point offrom 130 to 150° C.; a glass transition temperature (Tg) in the range offrom 75 to 90° C.; a weight-average molecular weight (Mw) in the rangeof from 500 to 1000 g/mole. In some embodiments, the hydrogenatedhydrocarbon resins can be non-migratory.

In some embodiments, the core layer can include migratory slip and/orantistatic additives in an amount of about 1-1000 ppm. In someembodiments, the core layer can be cavitated or pigmented to satisfy theend user's requirements such as color, opacity, density, etc.

The coextruded outer skin layer (A) designed for functionalities (i.e.,functional outer layer) could be formulated from polyolefin resins forthe application of heat-sealing, winding, adhesion, or printing. Thepolyolefin resins include ethylene homopolymer, propylene homopolymer,ethylene or propylene-based copolymers and terpolymers (e.g.ethylene-propylene, ethylene-butene, propylene-butene,ethylene-propylene-butene), or blends thereof. Modified polar polyolefinresins for instance as maleic-anhydride grafted polar polyolefins orcopolymerized polar polyolefin resins could also be added into the outerlayers to promote adhesion, particularly as a tie-resin or tie-layer forreceiving polar polymer coatings or coextruded layers.

The coextruded outer cold seal release layer (C) of the cold sealrelease film can be designed for both release and winding purposes. Asdescribed above, this layer can include a blend of materials offeringlow blocking force, low compatibility to the cold seal adhesive, lowCOF, and high scuff resistance. A higher MFR high crystallinepolypropylene resins may be required if orientation is a problem in thetenter oven as there exists a limitation to use processing aid such aslow ethylene content PB-1 polymers in the release layer. Additionally,the coextruded outer release layer (C) could be formulated to have amatte finish by adding a block copolymer blend of polypropylene and oneor more other polymers (e.g. polyethylene) to provide a roughened andlow gloss surface during the step of film formation. Anti-blocking andslip additives as described previously may also be added to this layerfor COF control.

Generally, film properties including the COF of the release layer,release force, and cold seal strength can be evaluated under bothambient and heat-aged conditions to determine the performance of a coldseal release film. Desirable anti-blocking and slip agents can includethose having low surface energy, and low adhesion/compatibility to coldseal adhesive, low stable COF under elevated temperature (i.e. hot slipCOF). Ideal surface polymers for the outer release layer can includethose which are incompatible with the materials in cold seal adhesivelayer.

The dynamic COF of the outer release layer of a cold seal release filmcan be in the range of from about 0.20 to 0.35 to provide goodmachinability in the downstream processes. In some embodiments, thestatic COF (μs) can be about 0.2-0.7, about 0.2-0.6, or about 0.2-0.35.In some embodiments, the dynamic COF (μd) can be about 0.15-0.5, about0.19-0.47, or about 0.2-0.35.

In some embodiments, a release force between the outer release layer andcold seal adhesive layer can be below about 100 g/in, below about 75g/in, or below about 50 g/in under both conditions of ambient andheat-aged 50° C. temperatures (forced heat-aging tests simulate therelease properties of the film after prolonged storage in a warehouse,for example). The cold seal strength can increase with increasingthickness of a cold seal adhesive layer. Usually, the cold seal strengthof the cold seal adhesive layer with a thickness of 3.2 g/ream can behigher than about 300 g/in or about 400 g/in after unwinding(traction-separation). For a cold sealable film having a thickness of3.6 g/ream cold seal adhesive layer, the cold seal strength can behigher than about 350 g/in or about 450 g/in.

In some embodiments, the surface of the outer release layer could betreated to crosslink the polymers and molecules on the top surface ofthe outer release layer and to reduce the tendency of forming cohesionwith cold seal adhesive layer. Surface treatments can be conducted byusing the high densities of energy flux, for example, corona, plasma,flame, and ion-electron beam treatment. Surface treatments may degradethe surface molecules of some polymers but crosslink the surfacemolecules of other polymers, depending on the chemistry structure ofpolymers on the outer layer. For example, surface treatments makepolyethylene and polydimethylsiloxane resins crosslinked on the topsurface layer. Crosslinking can increase glass transition temperature(Tg) and reduces motilities of polymer molecules on the top surfacelayer. After surface crosslinking treatment, the tendency of formingcohesion between the outer layer with polyethylene resins and the coldseal adhesive layer could be reduced greatly. Surface treatments may noteffectively crosslink polypropylene resins but instead may degradepolypropylene molecules on the top surface into low molecular weightspecies or sticky polypropylene debris which can undesirably induce highblocking force with the cold seal adhesive.

For a typical 3-layer coextruded film, the coextrusion process caninclude a three-layered compositing die. The polymeric core layer (B)can be sandwiched between the outer skin layer (A) and the outer releaselayer (C). The outer layer (A) of three layer laminate sheet can be castonto a chilling or casting drum with a controlled temperature in therange of from about 15 to 45° C. to solidify the non-oriented laminatesheet, followed by a secondary cooling on another chilling drum with acontrolled temperature. The non-oriented laminate sheet can be stretchedin the machine direction at about 95 to 165° C. at a ratio of about 4 to6 times of the original length and then heat-set at about 50 to 100° C.to obtain a uniaxially oriented laminate sheet with minimal thermalshrinkage. The uniaxially oriented laminate sheet can be introduced intoa tenter and preliminarily heated between about 130° C. and 180° C., andstretched in the transverse direction at a ratio of about 7 to 10 timesof the original length and then heat-set to give a biaxially orientedsheet with minimal thermal shrinkage. Surface discharge-treatmentdiscussed above may be applied to either layer A or layer C beforerewinding the film, depending on the film product design and applicationuse.

The total thickness of the coextruded cold seal release film afterbiaxial orientation could be in the range of from about 10 to 50microns, about 12 to 30 microns, or about 15 to 25 microns. Thethickness of any of the outer-most layers could be in the range of fromabout 0.25 to 4 microns, about 0.5 to 3 microns, about 0.5 to 2 microns,about 0.5 to 1.5 microns, or about 0.5 to 1.0 microns.

The biaxially oriented film may then be used for offline printing. Theprinted film may be laminated with a metallized barrier film which couldbe a metallized BOPP film or a polyester film with a cold seal adhesivereceiving layer opposite to the metallized or laminating layer. Afterlamination, a cold seal adhesive could be coated on the substrate withthe cold seal receptive layer; the cold seal adhesive layer can be driedat elevated temperatures and then the web may be rewound into a roll. Inthe wound laminated roll, the cold seal adhesive layer can directlycontact the cold seal release layer, which is opposite to the cold sealadhesive layer. The processes of printing, laminating, and coating couldbe conducted inline or separately in different lines. The rewound rollthen may be unwound in downstream sub-slitting process. The slit rollscan then be unwound to pack products at end user locations using anappropriate packaging machine.

This invention could be better understood with reference to thefollowing examples, which are intended to illustrate specificembodiments within the overall scope of the invention.

EXAMPLES Example 1

A 3-layer coextruded film was made on a nominal 1.6 m wide biaxialorientation line, comprising a core layer (B), an outer skin functionallayer (A) on one side of the core layer, and an outer skin cold sealrelease layer (C) on the other side of the core layer opposite that ofthe skin layer (A). The core layer comprised about 90 wt % TotalPetrochemical Co.'s Total 3273 HCPP resin and 10 wt % Oppera® PR100Ahydrocarbon resin (HCR, supplied by ExxonMobil; the HCR was melt blendedwith HCPP at 50/50 ratio). The skin layer (A) comprised about 80 wt %mini-random conventional polypropylene Total LX11203 andethylene-propylene copolymer Total 8473 supplied by Total PetrochemicalCo. and about 0.06 wt % Silton® JC-30 antiblock pre-blended into TotalLX11203 (Silton® JC 30 is an anti-blocking agent with nominal 3 μmparticle size of a spherical sodium calcium aluminum silicatemanufactured by Mizusawa Industrial Chemicals, Co., Ltd.). The outerrelease layer (C) comprised about 93.0 wt % Total 3571 conventionalpropylene homopolymer (Total 3571 has a melt flow rate of 9.0 g/10 min.(2.16 KG/230° C.), a melting temperature of 160° C., xylene solubles ofabout 3%, and isotacticity of <95%) and 7.0 wt % ABVT 242 SC. ABVT 242SC is a masterbatch of 5 wt % Tospearl® 120 particles in propylenecopolymer carrier resin, supplied by A. Schulman. Tospearl® 120 has anominal 2 μm particle size of a spherical cross-linked silicone polymersupplied by Momentive Performance Materials. The total thickness of this3-layer coextruded film after biaxial orientation was nominal 70G (17.5μm). The thickness of the outer skin layer (A) and outer release skinlayer (C) after biaxial orientation was nominal 3G (0.75 μm) and 4G (1.0μm), respectively. The thickness of the core layer (B) is nominal 63G(15.75 μm). The outer skin layers and core layer were melt-extruded atabout 230-260° C. The 3-layer coextrudate was passed through a flat dieto be cast on a chill drum of about 20-26° C. The formed cast sheet waspassed through a series of heated rolls at about 100-124° C. withdifferential speeds to stretch in the machine direction (MD) to a 4.75stretch ratio. This was followed by transverse direction (TD) stretchingto an 8.0 stretch ratio in the tenter oven at about 150-170° C. in atenter oven. Inside the tenter oven, there are three zones for thepurposes of heating, stretching, and heat-setting. The temperatures offirst, second, and third zones are about 165, 155 and 150° C.,respectively. After transverse stretching, the film was heat-set in thethird zone to minimize thermal shrinkage, followed by a 5% relax in thetransverse direction. The resultant laminate film was corona-dischargetreated upon the surface of the outer skin layer (A) before it was woundinto a roll form. The film was then tested for mechanical properties,printing, optical properties, COF, and cold seal release performanceunder ambient and heat aged conditions.

The outer release layer of the coextruded film made in Example 1 showedexcellent COF but very poor cold seal release properties. At ambientcondition, the release force was 219 g/in; and at heat-aged 50° C.condition, the release layer of the film was stuck to the cold sealadhesive layer of Dow Chemical COSEAL® 30061A and the film layers couldnot be separated. Cold seal deadening occurred due to the poor releaseperformance of the release layer.

Example 2

Example 2 was made using the same conditions as that of Example 1.However, the outer release layer was changed to comprising 93 wt % Total3571 conventional homopolypropylene resin and 7.0 wt % EverGlide®MB125-11Ultra supplied by Polymer Dynamix. The MB125-11 Ultra ispartially cross-linked polyalkylsiloxane produced with 25 wt % activecomponent of silicone gum by reactive extrusion compounding. Theparticle size of partially cross-linked silicone after the film is madeis predominately in the range of from 0.5 to 2 μm. The release layer ofthe coextruded film showed excellent COF but poor release performance.The partially cross-linked silicone particles in the outer release layerdid show good performance in COF control but did not provide sufficientrelease properties to the cold seal adhesive layer.

Examples 3-5

Examples 3-5 were made using the same conditions as that of Example 1.However, the outer release layer was changed to comprisingLyondellBasell Toppyl® PB8340M at the content of 20 wt %, 30 wt %, and40 wt % in the release layer (C), respectively. No change was made inthe content of the Tospearl® 120 particles in the outer release layer.The release layer showed slightly higher COF as PB8340M was increased inthe outer layer due to the soft characteristic of PB-1 in comparisonwith homopolypropylene Total 3571 resin. Compared to the coextruded filmmade in Examples 1 and 2, the outer release layer of the coextrudedfilms in Examples 3 to 5 with added PB8340M polymer showed much bettercold seal release performance at both ambient and heat-aged (50° C.)conditions. However, at the content of 20 wt % PB8340M, the releaseforce is relatively high and undesirable, the cold seal strength of thecold seal adhesive layer was also negatively impacted by poor releaseperformance after separation.

Example 6

Example 6 was made using the same conditions as that of Example 1.However, the core layer comprised about 100 wt % CH020-01homopolypropylene resin. No change was made to the outer skin layer (A).The outer release layer (C) was changed to comprising about 93.0 wt %CH020XK high crystalline propylene homopolymer (with xylene solubles <3wt % and isotacticity of >95%) and 7.0 wt % ABVT 242 SC (A. Schulman'sTospearl® 120 masterbatch). The outer release layer of the coextrudedfilm showed excellent COF, a cold seal release force in the acceptablerange to give good release performance at both ambient and heat-aged(50° C.) conditions. The cold seal strength of the cold seal adhesivelayer was not impacted by the release performance or deadened by therelease layer's composition.

Examples 7-10

Examples 7-10 were made using the same conditions as that of Example 6.However, the outer release layer was changed to comprisingLyondellBasell Toppyl® PB8340M at the content of from 2.5 wt %, 5.0 wt%, 10.0 wt %, and 40 wt % in the release layer, respectively. Thecontent of ABVT242 SC (Tospearl® 120 masterbatch) in the release layerof Example 7-9 was 4.0 wt %. The content of ABVT242 SC in the releaselayer of Example 10 was about 7.0 wt %. The content of HCPP in therelease layer was changed accordingly to meet the total 100 wt % in theouter release layer (C). The release layer of the Examples 7-9 showedexcellent COF and good release performance and cold seal strength. Theouter release layer of the coextruded film made in Example 10 showedslightly higher COF as PB8340M was increased to 40 wt % in the outerrelease layer and excellent release performance at both ambient andheat-aged conditions. As HCPP is predominately used in the outer releaselayer, even if the content of low ethylene containing PB-1 polymer wasas low as 2.5 wt %, the release layer of the cold seal release filmshowed very good release performance.

Examples 11-12

Examples 11-12 were made using the same conditions as that of Ex. 6. Theouter release layer (C) of Example 11 was changed to comprising 93 wt %CH020XK, 4.0 wt % ABVT 242 SC and 3.0 wt % EverGlide® MB125-11Ultra. InEx. 12, the partially crosslinked polydialkylsiloxane in the outerrelease layer (C) was replaced by 3.0 wt % Dow Corning HMB-6301, whichhas 25 wt % active component in homo-PP carrier resin. The outer releaselayer of the coextruded film made in Ex. 11 gave a release force of 24g/in and 49 g/in at both conditions of ambient and heat-aged 50° C.,respectively. After separation, the cold seal strength was 495 g/in and514 g/in, respectively. The release layer of the coextruded film made inthe Ex. 12 showed slightly higher release force and slightly lower coldseal strength.

Example 13

Example 13 was made using the same conditions as that of Ex. 11. Theouter release layer of Ex. 13 was changed to comprising 94 wt % CH020XK,4.0 wt % ABVT 242 SC and 2.0 wt % Dow Corning MB50-801. MB 50-801 is amasterbatch of 50 wt % silica treated high molecular weight siloxanepolymer in homo-PP carrier resin. The outer release layer of thecoextruded film made in Ex. 13 showed release forces at about 69/in and90 g/in for ambient and heat aged conditions, respectively. Slightlylower cold seal strength was also observed for the sample in Ex. 13. Itis possible that there could have been silicone oil residues oroligomers left inside the particles of partially high molecular weightsiloxane polymer; these residues and oligomers could have migrated tothe surface of the release layer (C) leading to a negative influence onthe cold seal release force and cold seal strength.

Examples 14-15

Examples 14-15 were made using the same conditions as that of Ex. 11except that the anti-blocking/slip agent in the outer release layer (C)was changed to comprising 4.0 wt % ABVT 242 SC and 5.0 wt % EverGlide®MB125-11 Ultra. No surface treatment was applied to the release layer ofthe film made in Ex. 14 while the release layer of the film made in Ex.15 was corona discharge-treated for comparison. Wetting tension of thecorona-discharge treatment of the selected surface was ca. 30-40dyne-cm/cm². The release layer of the film made in Ex. 14 showedexcellent release performance, the cold seal strength of the cold sealadhesive layer was very good too. However, the release layer of the Ex.15 was blocked to the cold seal adhesive layer due to surface dischargetreatment. In this example, the oxidative surface treatment on the HCPPrelease layer was found to negatively impact the release performance ofthe release layer to cold seal adhesive.

Examples 16-18

Example 16 was made using the same conditions as that of Example 6.However, the outer release layer was changed to comprising 52 wt % TotalHDPE9260, 40 wt % LyondellBasell Toppyl® PB8640M, 4.0 wt % ABVT 242 SC,and 4.0 wt % X116EPC. HDPE9260 is high density polyethylene, supplied byTotal Petrochemical Co., has a melt flow rate of 2.0 g/10 min. (2.16Kg/190° C.) and a density of 0.96 g/cm³. X116EPC is a masterbatch ofpartially cross-linked polyalkylsiloxane masterbatch in propylenecopolymer with 25 wt % active composition. The release layer of thecoextruded film made Example 116 showed excellent COF and good releaseperformance and cold seal strength.

Example 17 was made using the same conditions as that of Example 16.However, the release layer (C) was changed to comprising 88 wt % TotalHDPE9260, 5 wt % Toppyl® PB8640M, 4.0 wt % ABVT242 SC, and 3.0 wt %X116EPC. The outer release layer of the coextruded film showed low COF,and release forces of 53/gin and 139 g/in under both ambient and heataged conditions, respectively. The COF of the release layer was slightlylower as PB8640M loading was reduced from 40 wt % to 5.0 wt 0% in theouter release layer. The release performance of Example 17 was slightlyworse than that of Example 16, especially under heat-aged 50° C.condition.

Example 18 was made using the same conditions as that of Example 17. Nochange was made to the recipes and conditions except that the releaselayer of the coextruded film was corona discharge-treated forcomparison. Wetting tension of the corona-discharge treatment of theselected surface was ca. 30-40 dyne-cm/cm². It was found that at ambientcondition the release layer showed excellent release performance and thecold seal strength, while at heat-aged 50° C. condition, the releaselayer was blocked to the cold seal adhesive layer.

Examples 19-20

Examples 19-20 were made using the same conditions as that of Example16. The outer release layer (C) of the Examples 19 and 20 was changed tocomprising 86 wt % DOWLEX®2027G, 4.0 wt % Tospearl 120 MB (the same asin Example 16) and 10 wt % XI 16EPC. DOWLEX®2027G, supplied by DowChemical Co., is linear medium density polyethylene (MDPE) with a meltflow rate of 4.0 g/10 min. (2.16/190° C.) and a density of 0.94 g/cm³.The outer release layer of the film made in the Example 19 was notcorona discharge-treated while the release layer of the Example 20 wascorona discharge-treated. Wetting tension of the corona-dischargetreatment of the selected surface was ca. 30-40 dyne-cm/cm². The releaselayer of the coextruded film made in Example 19 was blocked to the coldseal adhesive layer at both ambient and 50° C. heat aged conditions.Adhesive failure occurred in the process of separation. The releaselayer of the film made in Example 20 showed excellent releaseperformance, the cold seal strength of the cold seal adhesive layer wasvery good after release—separation. The release performance wassignificantly improved with corona discharge-treatment in this set ofexamples using MDPE.

Examples 21-24

Example 21 was made using the same conditions as that of Example 16. Theouter release layer (C) was changed to comprising 56 wt % POLYBATCH® DUL3636 LTX-3, 40.0 wt % Toppyl® PB8640M, 4.0 wt % ABVT 242 SC. The DUL3636 LTX-3 was supplied by A Schulman as a proprietary matte finishmasterbatch. It is compatible with PP block copolymer, PP homopolymer,PP random copolymer, HDPE, LDPE and LLDPE.

Example 22 was made using the same conditions as that of Example 21. Theouter release layer was changed to comprising 66 wt % DUL363LTX3, 30.0wt % Toppyl PB8640M, 4.0 wt % ABVT 242 SC.

As a result of adding matte finish masterbatch into the outer releaselayer, the release layer has a rough surface and much lower gloss. Thecoextruded film also provided high haze property. No polydialkylsiloxaneadditive was added into the outer release layer. The total amount ofanti-blocking agent in the release layer is relatively low. The outerrelease layer of Example 22 showed slightly lower release force thanExample 21 and slightly higher cold seal strength after release.

Example 23 was made using the same conditions as that of Examples 21.The outer release layer was changed to comprising 56 wt % DUL 3636 LTX3,40 wt % Toppyl PB8640M, and 4.0 wt % X116EPC.

Example 24 was made using the same conditions as that of Example 23. Theouter release layer was changed to comprising 66 wt % DUL 3636 LTX3, 30wt % Toppyl 8640M and 4.0 wt % X116EPC.

The content of partially cross-linked polydialkylsiloxane particles inthe outer release layer was about 1.0% wt % in Examples 23-24 and noTospearl® 120 particle was added into the outer release layer. The outerrelease layer of the coextruded films Examples 23-24 has low COF and amatte finish. The outer release layer of the two film samples showedgood release properties at both ambient and heat-aged (50° C.)conditions.

Examples 25-26

Examples 25-26 were made using the same conditions as that of Example21. The outer release layer (C) was changed to comprising 56.0 wt %CH020XK, 36.0 wt % DOWLEX®2027G, 4.0% ABVT242SC and 4.0% MB125-11 Ultra.The outer release layer of the film in Ex. 25 was not coronadischarge-treated while the outer release layer of the film in Ex. 26was corona discharge-treated for comparison. Wetting tension of thecorona-discharge treatment of the selected surface was ca. 30-40dyne-cm/cm².

The outer release layer of the coextruded films Ex. 25 and 26 showed amatte finish similar to that seen Ex. 21-24, but a lower COF, comparedto Ex. 21-24 due to the high content in anti-blocking agents as well ashigh crystallinity of the polymers in the release layer. At ambientcondition, the release force of the outer release layer of Ex. 25-26 wasin the normal range desirable for cold seal release film, while atheat-aged 50° C. condition, both film samples showed high blockingforce, especially, corona treatment on the outer release layer withadded HCPP resin increased the blocking force and deteriorated cold sealperformance.

The following Tables provide the compositions and properties of Examples1-26 described above. In Table 1, Cony PP(conventionalpolypropylene)=Total 3271; HCPP (high crystallinepolypropylene)=Phillips 66 CH020XK; PE (polyethylene)=Total HDPE9260 orDowlex 2027G; PB-1 (polybutene)=Toppyl PB8340M or PB8640M; Matte MB(matte resin masterbatch)=Polybatch DUL3636 LTX-3; AB MB (antiblockadditive masterbatch)=ABVT 242SC; and SG MB (silicone gummasterbatch)=Everglide MB125-11 Ultra or X116EPC; or Dow CorningMB50-801.

TABLE 1 All components in wt % Example Conv PP HCPP PE PB-1 Matte MB ABMB SG MB 1 93 — — — — 7 — 2 93 — — — — — 7 3 73 — — 20 — 7 — 4 63 — — 30— 7 — 5 53 — — 40 — 7 — 6 — 93 — — — 7 — 7 —   93.5 —   2.5 — 4 — 8 — 91—  5 — 4 — 9 — 86 — 10 — 4 — 10 — 53 — 40 — 7 — 11 — 93 — — — 4 3 12 —93 — — — 4 3 13 — 94 — — — 4 2 14 — 91 — — — 4 5 15 — 91 — — — 4 5 16 —— 52 40 — 4 4 17 — — 88  5 — 4 3 18 — — 88  5 — 4 3 19 — — 86 — — 4 10 20 — — 86 — — 4 10  21 — — — 40 56 4 — 22 — — — 30 66 4 — 23 — — — 40 56— 4 24 — — — 30 66 — 4 25 — 56 36 — — 4 4 26 — 56 36 — — 4 4

In the following Table 2, PB-1 is the label of low ethylene-containingpolybutene-1 polymers; T120 is the label of Tospearl® 120 particles;X-Sil is the label of partially crosslinked polydialkylsiloxaneparticles or silica treated high molecular weight siloxane polymer; COFis the static and dynamic COF (μs and μd) of the outer release layer (C)of the coextruded films measured at ambient temperature; release force(grams/inch) was labeled as Rel. f. (g/in) and cold seal strength(grams/inch) was labeled as CSS (g/in). Both the release force and coldseal strength were measured at ambient temperature while the blockedsamples of the coextruded films were prepared in advance at eitherambient (22° C.) and heat aged (50° C.) conditions. “Blocked” in theTables means that the cold seal strength of the samples could not bemeasured effectively because the cold seal adhesive layer was extremelydeteriorated due to blocking. Treatment (A/C) indicated that the outersurface layer was corona discharge-treated at a power supply output of1.0 kilowatts on the outer functional layer (A) or on both outer layers(A/C).

TABLE 2 Active component (wt %) COF Ambient (22° C.) Heat aged (50° C.)Treatment Examples PB-1 T120 X-Sil μs μd Rel. f. (g/in) CSS (g/in) Rel.f. (g/in) CSS (g/in) (A/C) Ex. 1 0.35 0.25 0.24 219 479 Blocked A Ex. 21.75 0.25 0.21 192 527 Blocked A Ex. 3 20 0.35 0.35 0.29 95 599 154 451A Ex. 4 30 0.35 0.45 0.34 38 592 54 540 A Ex. 5 40 0.35 0.50 0.47 17 60041 619 A Ex. 6 0.35 0.30 0.21 66 584 59 550 A Ex. 7 2.5 0.2 0.28 0.22 30545 52 552 A Ex. 8 5 0.2 0.27 0.24 24 562 53 588 A Ex. 9 10 0.2 0.300.26 29 553 103 538 A Ex. 10 40 0.35 0.50 0.39 14 635 40 845 A Ex. 110.2 0.75 0.27 0.23 24 495 49 514 A Ex. 12 0.2 0.75 0.24 0.20 34 434 54448 A Ex. 13 0.2 1.0 0.25 0.21 89 421 90 412 A Ex. 14 0.2 1.25 0.28 0.2320 628 29 587 A Ex. 15 0.2 1.25 0.28 0.23 193 578 Blocked A/C Ex. 16 400.2 1 0.50 0.36 32 580 65 524 A Ex. 17 5 0.2 0.75 0.26 0.23 53 446 139234 A Ex. 18 5 0.2 0.75 0.29 0.23 27 499 Blocked A/C Ex. 19 0.2 25 0.300.28 Blocked Blocked A Ex. 20 0.2 25 0.31 0.26 13 615 78 579 A/C Ex. 2140 0.2 0.58 0.38 46 488 135 490 A Ex. 22 30 0.2 0.52 0.34 42 800 72 542A Ex. 23 40 1 0.31 0.29 25 571 48 582 A Ex. 24 30 1 0.27 0.28 23 521 38495 A Ex. 25 0.2 1 0.23 0.22 35 460 115 366 A Ex. 26 0.2 1 0.21 0.19 45488 Blocked A/CTest Methods

The various properties in the above examples were measured by thefollowing methods:

COF Test: The outer release layer (C) of the coextruded films made inExamples and was tested under ambient temperature condition to determinethe static and dynamic COF (μs and μd) using the method of ASTM D1894.

Wetting Tension Test: Wetting tension of the selected coronadischarge-treated surfaces were measured using the method of ASTM D2578.

Blocking Test: To achieve a good quality and consistent hand-drawdowncoatings of cold seal adhesives for easy handling and avoiding wrinkles,a stiff polyethylene extrusion-laminated template sheet was produced forblocking and cold seal strength test using Torayfan® biaxially orientedpolypropylene films TC01/60G and Torayfan® F62W/70G, which arecommercially available from Toray Plastics (America), Inc. Torayfan®TC01/60G is a two-side treated biaxially oriented polypropylene filmcomprising a core layer and two outer layers. Torayfan® F62W/70G isone-side treated biaxially oriented polypropylene film comprising a corelayer and two outer layers. The thickness of the LDPE extrudate adhesiveused in the lamination was about 10 #/ream and about 60G in thickness,the extrusion lamination was conducted at extrusion temperature 315° C.and lamination speed 500 ftpm. The laminate has a structure of TC01/10#LDPE/F62W and a total thickness of 210G. The corona treated side ofTC01 was laminated to F62W's discharge-treated printable side of thefilm; the exposed ultra-high surface energy (UHSE) side of the TC01 filmafter lamination was used as the cold seal receptive layer forhand-drawdown coating of the cold seal adhesive latexes. Dow ChemicalCOSEAL™ 30061A was used to prepare drawdown coating for blocking tests.The COSEAL™ 30061A cold seal adhesive is a water-based milky-whitesynthetic latex adhesive with a solids content of 59.1±1 wt %.

The hand-drawdown coating of the cold seal latex was applied using MayerRod #6 and COSEAL™ 30061A cold seal adhesive, which give a coat weightof about 3.5 to 3.7 #/ream. After the drawdown was complete, thelaminate template was dried in a 120° C. oven for 5 seconds and then thecoated template was cooled down in ambient temperature condition. Theouter release layer (C) of a cold seal release film test sample was thenpositioned to contact and stacked onto the cold seal adhesive coatedlayer of the laminate template. A maximum of 12 stacks separated by asheet of A4 paper of the stacked samples were inserted into a blockingjig for varying test conditions (The blocking jig was manufactured byKoehler Instruments Co.). The blocking area of the blocking jig was ca.1 inch diameter for a blocking area of ca. 0.785 sq. inches. Theconditions for ambient include that a temperature of about 22° C., 16hrs duration time, compression pressure 100PSI (the head of blocking jigon the stacked samples). Under heat-aged condition, the blocking jig wasput into an oven with a 50° C. setting temperature. The duration timeand compression pressure were the same as that of ambient condition.

After blocked samples were prepared under either ambient or heat-agedconditions described above, the blocked samples were cut into one inchwide stripes and then tested at ambient temperature using Instron™ (90°peeling angle) for measuring the force to separate the two test filmfrom the laminate template (aka the release force), averaging the dataof three blocked sample strips. The cold seal adhesive layer of theseparated samples was sealed to itself using a Sentinel™ Sealer underthe conditions of 80 PSI pressure/0.5 second dwell time/serratedjaws/ambient temperature. The sealed strips were tested for cold sealstrength using Instron™ tester, measuring the force to peel apart thecold-sealed films (aka cold seal strength).

Definitions

Unless defined otherwise, all terms of art, notations and othertechnical and scientific terms or terminology used herein are intendedto have the same meaning as is commonly understood by one of ordinaryskill in the art to which the claimed subject matter pertains. In somecases, terms with commonly understood meanings are defined herein forclarity and/or for ready reference, and the inclusion of suchdefinitions herein should not necessarily be construed to represent asubstantial difference over what is generally understood in the art.

Reference to “about” a value or parameter herein includes (anddescribes) variations that are directed to that value or parameter perse. For example, description referring to “about X” includes descriptionof “X”. In addition, reference to phrases “less than”, “greater than”,“at most”, “at least”, “less than or equal to”, “greater than or equalto”, or other similar phrases followed by a string of values orparameters is meant to apply the phrase to each value or parameter inthe string of values or parameters. For example, a statement that a filmhas at most about 10 wt. %, about 15 wt. %, or about 20 wt. % of acomponent is meant to mean that the formulation has at most about 10 wt.%, at most about 15 wt. %, or at most about 20 wt. % of a component.

As used herein, the singular forms “a,” “an,” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It is also to be understood that the term “and/or” as usedherein refers to and encompasses any and all possible combinations ofone or more of the associated listed items. It is further to beunderstood that the terms “includes, “including,” “comprises,” and/or“comprising,” when used herein, specify the presence of stated features,integers, steps, operations, elements, components, and/or units but donot preclude the presence or addition of one or more other features,integers, steps, operations, elements, components, units, and/or groupsthereof.

This application discloses several numerical ranges in the text andfigures. The numerical ranges disclosed inherently support any range orvalue within the disclosed numerical ranges, including the endpoints,even though a precise range limitation is not stated verbatim in thespecification because this disclosure can be practiced throughout thedisclosed numerical ranges.

The above description is presented to enable a person skilled in the artto make and use the disclosure, and is provided in the context of aparticular application and its requirements. Various modifications tothe preferred embodiments will be readily apparent to those skilled inthe art, and the generic principles defined herein may be applied toother embodiments and applications without departing from the spirit andscope of the disclosure. Thus, this disclosure is not intended to belimited to the embodiments shown, but is to be accorded the widest scopeconsistent with the principles and features disclosed herein.

The invention claimed is:
 1. A method of forming a cold seal releasefilm comprising: coextruding a laminate comprising: a core layercomprising polypropylene; a first outer layer on a side of the corelayer comprising polyolefin resin; and a second outer layer on a side ofthe core layer opposite the first outer layer consisting of 53-93.5 wt.% high crystalline polypropylene having an isotactic content greaterthan 95%; 2.5-40 wt. % polybutene-1; incompatible propylene polymers orblock copolymers of propylene; and 1000-5000 ppm spherical anti-blockingagents; and biaxially orienting the coextruded laminate.
 2. The methodof claim 1, wherein the polybutene-1 is low ethylene-containingpolybutene-1.
 3. The method of claim 2, wherein the lowethylene-containing polybutene-1 has an ethylene content of less than 2mol %.
 4. The method of claim 2, wherein the low ethylene-containingpolybutene-1 has a melt flow rate of 2 to 6 g/10 min.
 5. The method ofclaim 1, wherein the spherical anti-blocking agents comprise at leastone of crosslinked silicone polymers and synthetic SiO2.
 6. The methodof claim 1, wherein the second outer layer has a dynamic coefficient offriction of 0.20-0.35.
 7. The method of claim 1, wherein thepolypropylene in the core layer is high crystalline polypropylene. 8.The method of claim 1, wherein the core layer comprises 2.5-25 wt. %hydrogenated hydrocarbon resins.
 9. The method of claim 1, wherein thecore layer comprises 1-1000 ppm of antistatic additives.
 10. The methodof claim 1, wherein the polyolefin resin comprises ethylene homopolymer,propylene homopolymer, ethylene or propylene-based copolymers andterpolymers, or blends thereof.
 11. The method of claim 1, furthercomprising discharge-treating a side of the second outer layer oppositethe core layer using high densities of energy flux.
 12. The method ofclaim 1, further comprising discharge-treating a side of the first outerlayer opposite the core layer.